Research ArticlePhysiology

Platelets contribute to amyloid-β aggregation in cerebral vessels through integrin αIIbβ3–induced outside-in signaling and clusterin release

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Sci. Signal.  24 May 2016:
Vol. 9, Issue 429, pp. ra52
DOI: 10.1126/scisignal.aaf6240

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Antiplatelet drugs for Alzheimer’s patients

Patients with Alzheimer’s disease (AD) often have pathological amyloid-β (Aβ) plaques in the brain parenchymal tissue and in cerebral blood vessels with adhesive or aggregated platelets. In the blood vessels, Aβ aggregates cause the vascular dysfunction disorder cerebral amyloid angiopathy (CAA), which contributes to AD progression. Donner et al. found that Aβ bound and stimulated the integrin αIIbβ3 on cultured human and mouse platelets, creating a feed-forward loop involving the secretion of clusterin and adenosine diphosphate, which in turn promoted Aβ aggregation and perpetuated platelet activation, respectively. Treatment with the platelet activation inhibitor clopidogrel decreased CAA burden in AD model mice, suggesting that antiplatelet therapy might ameliorate vascular symptoms contributing to dementia in AD patients.

Abstract

Cerebral amyloid angiopathy (CAA) is a vascular dysfunction disorder characterized by deposits of amyloid-β (Aβ) in the walls of cerebral vessels. CAA and Aβ deposition in the brain parenchyma contribute to dementia and Alzheimer’s disease (AD). We investigated the contribution of platelets, which accumulate at vascular Aβ deposits, to CAA. We found that synthetic monomeric Aβ40 bound through its RHDS (Arg-His-Asp-Ser) sequence to integrin αIIbβ3, which is the receptor for the extracellular matrix protein fibrinogen, and stimulated the secretion of adenosine diphosphate (ADP) and the chaperone protein clusterin from platelets. Clusterin promoted the formation of fibrillar Aβ aggregates, and ADP acted through its receptors P2Y1 and P2Y12 on platelets to enhance integrin αIIbβ3 activation, further increasing the secretion of clusterin and Aβ40 binding to platelets. Platelets from patients with Glanzmann’s thrombasthenia, a bleeding disorder in which platelets have little or dysfunctional αIIbβ3, indicated that the abundance of this integrin dictated Aβ-induced clusterin release and platelet-induced Aβ aggregation. The antiplatelet agent clopidogrel, which irreversibly inhibits P2Y12, inhibited Aβ aggregation in platelet cultures; in transgenic AD model mice, this drug reduced the amount of clusterin in the circulation and the incidence of CAA. Our findings indicate that activated platelets directly contribute to CAA by promoting the formation of Aβ aggregates and that Aβ, in turn, activates platelets, creating a feed-forward loop. Thus, antiplatelet therapy may alleviate fibril formation in cerebral vessels of AD patients.

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